1. Field of the Invention
This invention relates to a composite building material, and more particularly to a building material incorporating a lightweight core and one or more fiber cement skins formed on opposite sides of the core.
2. Description of the Related Art
Fiber-reinforced cement products such as water-resistant building sheets have been used for building since 1895. In recent history, reinforcing fibers used in such products have included not only asbestos fibers, but also cellulose (wood) fibers (see Australian Patent No. AU 515151), metal fibers, glass fibers and other natural fibers. Typically the density of such building sheets is from 1.2-1.7 g/cm3, the variation in density typically being achievable by compression and dewatering of the fiber cement slurries used in manufacture, and by varying the amount of fiber used.
The densities of fiber cement described above mean the products are heavier than timber-based products of equal dimension and are more difficult to cut, machine and nail than timber and timber-based products. The density of lumber typically ranges from 0.7-0.9 g/cm3 for dry hardwoods and from 0.38-0.6 g/cm3 for dry softwoods. Thus, a fiber cement material of density similar to lumber would enable products to be manufactured that were lighter, more nailable, easier to cut, and easier to machine, while retaining the durability, fire-resistant, rot-resistant, and water-resistant properties of fiber cement.